The present invention relates generally to gas metal arc welding. More particularly, the present invention relates to a composition and properties of a family of consumable electrodes for gas metal arc welding of carbon steels.
The growing demand for increased electric arc welding productivity calls for continuing efforts to reduce welding time while improving productivity of structural fabrication, especially for the robotic applications. In order to operate a robotic welder at its maximum capacity, welding consumables should be able to provide good welding beads at the maximum travel speed without increasing the number of welding defects. One of the approaches to improve the productivity and reduce the welding time would be to increase the deposition rate and travel speed for a given weld size. Unfortunately, it often happens that an increase in a travel speed of a welding process is accompanied by an increase in the number of welding defects.
Another approach to solving the problem is to try to manipulate the composition and structure of a welding electrode to change its properties in such a way that the deposition rate and travel speed of a welding process will increase advantageously. The electric arc welding process often uses metal consumable electrodes in the form of tubular welding wires. These metal core welding wires are usually made of generally tubular composites having a metal sheath and a core made of various powdered materials. The known tubular types of wires can be classified as metal core wires or flux-core wires. Metal core wire electrodes, with relatively simple chemical composition and known metallurgy, have a high deposition rate and high deposition efficiency while producing less slag, and, therefore, are increasingly used as an alternative to solid or conventional flux core wires for improved productivity in structural fabrication. If higher deposition rates exhibited by metal core wires could be combined with a high travel speed and a good quality welding bead, a welding electrode having such a metal core wire would greatly increase the productivity of arc welding used in many applications in the automotive, shipbuilding and general fabrication industry.
Conventional metal core wires of the type described in a number of U.S. Patents relate to different types, structures or combinations of elemental composition of welding electrodes. For example, U.S. Pat. No. 3,656,918, relates to an alloy suitable for use as a weld-filler material with about 2% of Mo as one the alloying elements in combination with Cr and Ni. U.S. Pat. No. 3,635,698 relates to a weld-filler metal made of a low alloy steel alloyed by a combination of Ni, Cr and Mo. U.S. Pat. No. 4,782,211 relates to a cluster welding electrode assembly having a rod covered with a flux alloyed by defined amounts of Mo and W. That Patent mentions that controlled amounts of tungsten, preferably in the form of a ferrotungsten alloy, appear to modify the working characteristics of the weld metal. U.S. Pat. No. 5,523,540 relates to a welding electrode of a composition within certain elemental composition ranges. The welding electrodes of that Patent form weld deposits with a low carbon bainitic ferrite microstructure of sufficient strength for welding high-strength steels. U.S. Pat. No. 5,824,992 relates to a metal-core wire with a core composition between approximately 2.5-6.0% or 2.5-12% of the total weight of the metal-core wire.
Manufacturing of a metal core wire normally involves forming, filling and then drawing or rolling the wire. First, a steel sheath is formed and bent into a U-shape tube, then an amount of metal powder, such as iron powder, is fed into the U-shaped tube. The subsequent forming and drawing process encloses and compacts the powder to form a wire and reduces that wire to its final shape. If an improved metal-core wire with a higher deposition rate and travel speed manufactured as described above could be provided, the productivity of the robotic arc welders could be significantly increased.
It is therefore an object of the present invention to provide a metal core wire and a method of manufacturing such a wire allowing an 15-20% increase in the deposition rates.
It is also an object of the present invention to provide a composition of a metal core wire electrode leading to a 45-50% increase in the welding electrode travel speed.
It is also an object of the present invention to provide carbon steel composite core wires exhibiting a combination of high melting points and appropriate surface tension of the molten wire, which combination leads to a high deposition rate and travel speed in the welding process.
The present invention is a weld wire comprising a sheath encapsulating a metal core made of powdered metal, wherein a fill percentage of the metal core is no less than approximately 12%. The metal core comprises a core composition alloyed with an alloying element or an combination of elements comprising Cr, Mo, V, W, Hf and Nb or combinations thereof, wherein a total weight percentage of the alloying element or the combination of elements in the core composition does not exceed approximately 1%. In a particular embodiment, the alloying element is Mo in the amounts selected from the range of about 0 to about 0.5 percent by weight and the fill percentage of the metal core is selected from the range of about 12% to about 30%. In a particular embodiment of the invention, the total percentage of the combination of elements is selected from the range of about 0.4% to about 0.8%.
To achieve a 15-20% increase in the deposition rates of the wires, the present invention provides a sheath encapsulating a steel core having a core fill percent of more than 12% and the steel core having a composition comprising an alloying element selected from the group consisting of Cr, Mo, V, W, Hf and Nb and combinations thereof. The deposition rates of such wires increases with the increase of the core fill percent, when the wire is used in the welding process. In particular, the deposition rate increases from about 15 lb/hr for the core fill percent of about 12% to the deposition rate of about 20 lb/h for the core fill percent of about 30%. In particular embodiments, a total weight percentage of Mo varies from about 0% to about 0.4%, and a total weight percentage of an alloying element does not exceed approximately 1%.
To achieve a 40-50% increase in the travel speed, the wire of the present invention comprises a sheath encapsulating a metal core, wherein a core fill percent of the metal core is higher than 12%, the metal core having a composition alloyed with an alloying element or an combination of elements comprising Cr, Mo, V, W, Hf and Nb or combinations thereof, wherein a total weight percentage of the alloying element or the combination of elements in the core composition does not exceed approximately 1%, and wherein a travel speed of the weld wire when used in welding ranges from about 65 in/min to about 145 in/min. The travel speed of the wire when used in welding can be characterized via a maximum travel speed ranging from about 80 in/min to about 145 in/min for the core fill percent ranging from about 12% to about 30%. The maximum travel speed of the wire measured during the welding experiments of the present invention corresponded to the composition comprising a percentage of Mo ranging from about 0% to about 0.4%.
A method of manufacturing a weld wire comprises forming a sheath into a shape which can be filled with a metal powder; filling the sheath with the metal powder, the metal powder having a composition alloyed with an alloying element or an combination of elements comprising Cr, Mo, V, W, Hf and Nb or combinations thereof, wherein a total weight percentage of the alloying element or the combination of elements in the core composition does not exceed approximately 1%. Further in the manufacturing process the metal powder is compacted to form a metal core; and the wire is drawn to achieve a core fill percentage of the metal core no less than 12%. According to the invention, the core fill percentage ranges from about 12% to about 30%, the alloying element is Mo ranging from about 0% to about 0.4%. The total weight percentage of the combination ranges from about 0.4% to about 0.8%.
These and other objects, features and advantages of the present invention will become more fully apparent upon consideration of the following detailed description of the invention with the accompanying drawings.